Means for wetting surfaces



March 20', 1962 E. P. WHITLOW 3,025,685

MEANS FOR WETTING SURFACES Filed Feb. 3, 1960 INVENTOR EUGENE F? WHITLOW ZW MQQ W ATTORNEY United States Patent Ofiice 3,025,685 Patented Mar. 20, 1962 3,025,685 MEANS FOR WETTING SURFACES Eugene P. Whitlow, Benton Harbor, Mich, assignor to Arkla Industries line, a corporation of Delaware Filed Feb. 3, 1960, Ser. No. 6,547 8 Claims. (Cl. 62-515) The present invention relates to novel means for wetting surfaces with a liquid having wetting characteristics.

In the illustrative embodiment of the invention, to be described in detail hereinbelow, the invention is shown as being applied to heat transfer apparatus, and more particularly to the wetting with refrigerant of the evaporator tubes in an evaporator cooling unit used in conjunction with a refrigeration apparatus. While the invention is particularly suitable for this purpose it will be appreciated that it may be used for other purposes where it is important to obtain the complete wetting of tubular surfaces.

As is well known, refrigerating apparatuses, as for example an absorption refrigerator, serve to cool whatever place is desired by removing heat from a heat transfer medium which circulates through the place to be cooled. One means for removing heat from a heat transfer medium, which may, for example, be water, is an evaporator cooling unit. Conventionally, such a cooling unit usually comprises a plurality of interconnected evaporator tubes horizontally disposed within the unit in vertical and horizontal rows. Cooling fluid or refrigerant often, but not necessarily, water, is allowed to flow or drip over the evaporator tubes, by means of drippers disposed above the uppermost tube in each vertical row, to cool the water or other suitable heat transfer medium being pumped through the tubes. Through the evaporation of the low temperature refrigerant or cooling liquid disposed on the outside surfaces of the tubes, heat is removed from the heat transfer medium Within the tubes in an amount proportional to the total heat of vaporization absorbed by the cooling liquid as it is evaporated.

In order to achieve the maximum cooling efiiciency of the evaporator cooling unit, it is necessary to keep the entire surface of the evaporator tubes wet with the cooling liquid at all times. To date, one method of doing this is by first distributing the cooling liquid evenly over the top rows of evaporator tubes, then providing drippers on each of the tubes so that an even distribution of water is maintained down the depth of the unit from each tube to the next tube therebe neath, and then providing capillary grooves on the surfaces of all of the tubes so that the cooling liquid will spread about the circumference of the tubes.

While this method has been found to be generally satisfactory, the present invention greatly increases the efficiency of it. The primary disadvantage of the normal capillary-grooved tube is that the cooling liquid does not spread out longitudinally along the tube from one groove to another, but simply spreads around the tube in the groove or grooves in which the drop of liquid was originally received. This, of course, means that a very large number of drippers are necessary if it is desired to wet the entire surface of the tube and all of the grooves. Furthermore, if in the conventional unit drippers are not provided on each tube, the dripping from each tube to the next tube below it will be random in nature and will not necessarily provide an even distribution of cooling liquid thereto.

The fact that conventional evaporator units to be efficient must be provided with a very large number of drippers, means that they necessarily must be quite complicated, and consequently quite expensive. The large number of drippers is necessitated by the fact that the conventional capillary-grooved evaporator tube cannot spread the cooling liquid longitudinally along the tube to grooves not in the path of one of the drippers. Since most presently known drippers are in the form of special devices themselves, the providing of all the evaporator tubes with such devices, in order to wet lower tubes, represents a substantial cost and renders the unit quite complicated.

It is therefore a primary object of the present invention to provide a highly efiicient means for wetting surfaces, particularly adapted to application with respect to evaporator tubes for use within an evaporator cooling unit, wherein the entire surface of each of the tubes is completely wetted by the cooling liquid, even though it be supplied to a single point on the surface of each of the tubes.

It is a further object of the present invention to provide a wetting means for evaporator tuba adapted for use in an evaporator cool-ing unit, wherein the entire surface of all the evaporator tubes in the unit may be wetted using a minimum number of drippers.

It is yet another object of the present invention to provide wetting means for an evaporator tube wherein it is possible to completely wet the entire surface of the tube by supplying a cooling liquid at only one point on the surface thereof, and wherein there is provided extremely simple means for establishing drip points on the tube, if desired, without effecting the wetting efficiency thereof.

It is a further object of the present invention to provide an evaporator tube having practical, economical and extremely simple means for forming drip points on the tube itself.

It is yet a further object of the present invention to provide an evaporator tube having simple means for causing cooling liquid dropped on one end of the tube to flow the full length of the tube to thereby wet the entire surface of the tube.

These and other objects of the present invention will become apparent from consideration of the following specification taken in connection with the accompanying drawings in which I have shown two embodiments of my invention by way of example, and wherein:

FIGURE 1 is a side elevational view of a portion of an evaporator tube embodying the principles of the present invention;

FIGURE 2 is an enlarged transverse sectional view taken along line 22 of FIGURE 1;

FIGURE 3 is an enlarged transverse sectional view taken along line 33 of FIGURE 1;

FIGURE 4 is an enlarged partial sectional view of part of the evaporator tube shown in FIGURE 1; and

FIGURE 5 is a side elevational view partly in section of a second embodiment of an evaporator tube embodying the principle of the present invention.

Referring more particularly to the drawings, there is shown in FIGURES 1 through 4 a portion of an evaporator tube, designated generally at 10, embodying the principles of the present invention. The outer surface of evaporator tube It) is provided with a plurality of helically disposed fins 12. As will be understood, these fins 12 are provided on the surface portion of the tube 16* which is intended to be exposed to the cooling liquid. The fins 12 are very closely spaced and define helically disposed capillary grooves 14 therebetween, as can be seen.

As is well known in the art, it is desirable to provide the tube with as many capillary grooves as is possible, in order to maximize the cooling efiiciency of the evaporator tube. This, of course, means that the grooves should be disposed as close to each other as is possible. In the preferred embodiment shown in FIGURES 1 through 4 the fins 12 and capillary grooves 14 are disposed in a helical configuration, however, it should be noted that there may be provided any number of continuous single capillary grooves 14 as is desired, depending upon the pitch of the helix and the width of the grooves.

The fins 12 may be formed integrally with the tube 10, as is shown, or may be provided in the form of separate fin members which are secured to the tube 10 in any conventional manner, as for example by soldering or welding. There are a number of ways in which the grooves 14 and fins 12 may be integrally formed about the circumference of the tube 10. For example, they may be formed by means of rolling, wherein a rolling tool is forced against the side of the tube 10 as it is rotating to thus form the grooves 14 by actually displacing the surface material of the tube 10 into fin formations, having grooves defined therebetween. This rolling technique as applied to forming capillary grooves in evaporator tubes is disclosed in US. Patent No. 2,645,954, issued July 21, 1953. Alternately, the capillary grooves 14 and fins 12 may be formed by means of a cutting process, as by means of a lathe or other similar machine.

The spacing between the fins 12 depends upon the diameter of the tube on which they are formed, but, in any case, it is important that they be close enough together that the spacing between any two adjacent fins can pull water by capillary action" from the bottom of the tube to the top of the tube, when the tube is disposed in a horizontal position. As will be understood, the larger the tube the closer the fin spacing must be in order to pull the cooling liquid the greater distance. Thus, any water or other cooling liquid which comes into the contact with the tube will, by means of grooves 14, be pulled around the entire circumference of the tube at that point.

While the fins 12 of the preferred embodiment are disposed in a helical configuration, this is not essential, and, if desired, they may be disposed in a circumferential plane perpendicular to the longitudinal axis of the tube, as is shown at 12 in FIGURE 5. In addition, it is not essential that the grooves be V-shaped as illustrated in FIGURES 1 through 4, but they may be of a rectangular shape, as indicated at 1 4' in FIGURE 5. The operating characteristics of the present evaporator tube, as will be described hereinafter, will not be aifected in any way by manufacturing the evaporator tube in accordance with FIGURE 5, rather than in accordance with FIGURES 1 through 4. As will be apparent, the modified evaporator tube design shown in FIGURE 5 may be manufactured in the same manner as the embodiment shown in FIG- URES 1 through 4, set forth above.

In addition to grooves 14 and fins 12, the tube is provided with a longitudinally disposed groove 16. The groove 16 is formed of a depth substantially equal to the depth of groove 14 and, as illustrated, is disposed on the lower edge of tube 10.

The purpose of the longitudinal groove 16 is very important and is as follows. When water or other cooling liquid drips onto the upper surface of tube 10 is is pulled around the entire circumference of the tube by capillary grooves 14. In the absence of a longitudinal groove, if water is allowed to drip on a tube of this type it will fill only the grooves into which it is allowed to drip. However, when a longitudinal groove is provided at the bottom of the tube it will serve to carry the water or cooling liquid from one capillary groove 14 to the next adjacent one and so on the full length of the tube 10. Therefore, water dripping onto the tube at any single point is carried around the tube at that point by the capillary grooves 14 and into longitudinal groove 16, at the bottom of the tube. The longitudinal groove 16 carries the liquid the full length of the tube 10 and into all of the remaining circumferential grooves 14, whereupon these remaining unwetted capillary grooves 14 pull the liquid from longitudinal groove 16 around the tube 10 to therefore wet it in its entirety. Once the tube has been completely wetted, excess cooling liquid supplied to the surface thereof simply drips down to the next adjacent tube to wet and thereby cool it. Since with this longitudinal groove 16 the tube 16 can be completely wetted by applying refrigerant at only one dripping point, distribution of the cooling liquid or refrigerant at the top of the tube becomes less critical. Therefore, it is not essential that drippers be provided on the tube, since other lower tubes in the cooling unit will be wetted completely regardless of the point from which the excess liquid on the next upper tube drips.

The longitudinal groove 16 is preferably located at the bottom of the tube 10, but it will function, as described above, at other positions around the circumference of the tube. The one consideration which is important if the groove 16 is to be moved from the bottom of tube 10, is that it be made narrower the closer it gets to the top of tube 10. Thus, if it is disposed at the very top of tube 10 it must be quite narrow, otherwise the weight of the water disposed therein would tend to cause it to flow out of the groove and around the tube to the bottom thereof. The groove 16 may be formed in any conventional manner, as by milling or broading.

In the embodiment illustrated, the evaporator tube 10 is also provided with a plurality of indentations 18 at the lower edge thereof, centered in longitudinal groove 16. The purpose of indentations 18 is to define definite dripping positions on the tube 10, whereby water, in excess of that needed to fill all grooves 14, dropped onto the tube will drip therefrom at predetermined points to the next evaporator tube disposed therebelow, to thereby cool it. The indentations 18 also prevent excess water or liquid from flowing longitudinally through groove 16 the full length of the tube 10 and out the end of the evaporator unit if the tubes are not disposed in a level position.

In the conventional type of evaporator unit in which evaporator tube 10 is to be used, there are usually provided within the unit a plurality of such tubes, all in communication and disposed one above the other. The uppermost tube receives the refrigerant or cooling liquid from drippers located at the top of the unit which are supplied with the cooling liquid. The liquid received from the drippers, of which there need be very few with the present invention, then flows through grooves 14 and longitudinal groove 16 to cover the entire tube within the unit. Excess water from this uppermost tube then drips onto the next lower tube, from the indentations 18, if they are provided, and so on until all the tubes in the evaporator unit are fully wetted. It should be noted that the indentations 18 are not essential to the operation of the cooler unit since the tubes will be fully wetted even though dripped on from only one point. However, they do make possible a more even distribution of the liquid on each tube in a quicker manner, and also eliminate the necessity for making sure that all of the tubes are level.

As can be seen in FIGURE 3, indentations 18 mash somewhat the longitudinal grooves 16 so as to restrict it, as indicated at 20. This restriction 20, as well as the fact that the liquid has an uphill path into the indentations, are instrumental in establishing the definite dripping points. As shown in FIGURE 2, the indentations 18 do not materially restrict the flow of fluid through the interior 22 of the tube. It should be apparent that if the longitudinal groove 16 is disposed on the tube 10 at a position other than at the bottom thereof, indentations 18 would probably not be feasible. In any case, as mentioned above, they are not essential to the operation of the present evaporator tube.

In one actual working model of the embodiment of the evaporator tube illustrated, the material used consisted of copper tubing, type DI-IP, B75 hard temper. The copper tubing was .585 inch in outside diameter, was .082 inch thick, and was 33% inches long. The grooves provided thereon were of the V-type, having an included angle inthe range of 25 to 45, and were provided 40 to the inch the entire length of the tube. The grooves were .013 inch deep. The longitudinal groove 16 was located at the bottom of the tube and was .0625 inch wide and .013 inch deep. The indentations 18 were provided at the bottom of the tube, centrally disposed on longitudinal groove 16, and each had a radius of inch, measured from a center disposed in the plane of the surface of the tube. The indentations 18 were disposed equally spaced upon the tube and were located every 3 inches along the tube starting '/e inch from the end thereof.

These dimensions are disclosed as being exemplary of one possible embodiment of a practical device, here an evaporator tube, which embodys the principles of the present invention.

While the exemplary embodiment described and illustrated relates to my novel wetting means in conjunction with an evaporator unit, it will be understood by those skilled in the art that it is ideally suited to use with many other types of apparatus. For example, it may be applied to the surfaces of the cooling tubes in a conventional absorber unit, such as the type forming a part of an absorption refrigerating apparatus. In such a unit it is desirable to spread out the absorbing fluid as much as possible to present a maximum surface area of the absorbing fluid to the surrounding substance to be absorbed. Since the absorption reaction is usually exothermic the absorbing fluid is usually disposed on the surface of tubes having a coolant flowing therethrough; thus, the wetting means of the present invention is ideally suited to such an application.

Another apparatus in which the present wetting means may be used is a gas absorption apparatus, wherein a gas is to be absorbed by a liquid. Here, a member provided with the present wettting means is completely wetted with the liquid and then exposed to the gas to be absorbed. Since the wetting means serves to maximize the surface area of the absorbing liquid, maximum absorption efficiency may be obtained.

In any of the possible applications of the present invention, it is not necessary that the outside .of a tubular surface be used. The invention is also ideally suited to the provision of wetting means on the inside of a tubular surface or member. In such an application the inside of a tube would be provided with a plurality of helical or circumferential capillary grooves, and a longitudinal groove substantially transverse thereto. Nor is it necessary that the surface to be wetted even be tubular. For example, a flat surface may be easily wetted in its entirety from a single point supply of liquid by providing it with a plurality of substantially parallel grooves, and another groove generally transverse thereto to distribute the liquid from the capillary grooves having liquid to all of the remaining ones. If the fiat surface is to be horizontally disposed, a transverse groove may be provided at each end of the surface, or if to be inclined, near the lower end thereof with the capillary grooves disposed thereon in a generally vertical direction. In all such applications the principle of operation of the wetting means is the same as that of the exemplary embodiment shown and described.

In any case, it will be understood by those skilled in the art that the specific details of construction and arrangement of elements, as described, are by way of example only and are not to be construed as limiting the scope of the invention. Since the invention relates to any of the numerous applications wherein it is desirable to maximize the surface area of a liquid and/or completely wet the surface of a given member, I, therefore, do not wish to be limited to the precise details set forth and intend that the invention embody all such features and modifications as are Within the scope of the appended claims.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1. Means for wetting a surface with a liquid, comprising: means defining a surface adapted to be wetted; a plurality of capillary grooves disposed on said surface,

each of said capillary grooves extending in substantially the same direction thereon; and groove means disposed on said surface transverse to said capillary grooves, whereby liquid supplied to said surface will be carried by capillary action the length .of the capillary grooves into which it was supplied and into said transverse groove means, to be carried thereby to the remaining capillary grooves which will in turn carry the liquid by capillary action to wet the entire area of said surface provided with said grooves.

2. Means for wetting as claimed in claim 1, wherein said transverse groove means and said capillary gropves are of substantially equal depth.

3. Means for wetting as claimed in claim 1, wherein said surface defining means is a tubular member, said capillary grooves are disposed around said tubular member, and said transverse groove means is disposed parallel to the longitudinal axis of said tubular member.

4. Means for wetting a tubular surface with liquid comprising: tube means; fin means disposed about the outer surface of said tube means to define capillary groove means associated with said tube means for maintaining the entire outer surface of said tube means wetted by a liquid; and means forming a part of said tube means for distributing liquid from a portion of said capillary means which has liquid to a portion of said capillary means which has insufficient liquid, whereby the entire surface of said tube means may always be evenly wetted.

5. Means for wetting the outside of a tubular surface, comprising: tube means; fin means disposed about the outer surface of said tube means to define capillary groove means around said tube means for maintaining and carrying a liquid on said tube means; and means defining a longitudinally disposed groove on said tube means for distributing liquid from a portion of said capillary means which has liquid to a portion which has insufiicient liquid, whereby the entire surface of said tube means having said capillary groove means may be covered with said liquid.

6. Means as claimed in claim 5, wherein said longi tudinal groove is of the same depth as said capillary groove means.

7. Means as claimed in claim 5, wherein said capillary groove means comprises at least one helical groove about said tube means.

8. Means as claimed in claim 5, wherein said longitudinal groove is disposed at the bottom of said tube means.

References Cited in the file of this patent UNITED STATES PATENTS 256,550 Davis Apr. 18, 1882 512,175 Faulkner Jan. 2, 1894 2,896,426 Ayling July 28, 1959 FOREIGN PATENTS 1 4 Gre r ta n 52 

